Engine Expert ???

I've an YIO-320 with Vetterman exhaust pipes; AFS EGT probes.
Per the AFS instructions, the EGT probes should be mounted between 2.5" and 3.5" from the exhaust pipe mounting flange.
Because the Vetterman pipes have an attachment bracket on the # 3 cylinder pipe that forces the installation of the EGT probe at the absolute minimum of 2.5" all four probes are, of course installed at that distance.

Now the question: What is the EGT variance from 2.5", 3.0", and 3.5"? I understand the temperatures further from the exhaust flange will be (significantly) lower but by how much? Since I have to mount the probes at the bare minimum, what should I be setting my EGT to for best leaning?

According to Lycoming the yellow zone is 1400 and max is about 1450. But where is that measured from?
So, if I adjust my EFIS to a higher set of EGT numbers, because my probes will be much closer to the flame, what should those settings be?

At this point, I try to lean to an EGT (# 1 cylinder always hottest) of 1398. But I feel I am burning too much fuel...

Suggestions from the engine experts is greatly appreciated.

You should totally ignore the absolute value of the numbers, for exactly the reasons you stated. The exception is if you have a turbocharger (blade temperature limits). You should be looking where each cylinder peaks as you lean, and set the mixture relative to that. E.g., best power, about 125 F rich side of peak; Lycoming recommended (and strongly not recommended by many) cruise 50 F rich of peak; best economy, lean of peak if your engine will run smoothly there; etc.

The negative of installing them closer to the flange is a potentially shorter probe life. Being closer to the flange, IMO, means you'll have more accurate temps but, as Bob said, the actual values are not all that meaningful.

622BH said:

Now the question: What is the EGT variance from 2.5", 3.0", and 3.5"?

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It doesn't matter.

Since I have to mount the probes at the bare minimum, what should I be setting my EGT to for best leaning?

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First, there is no "best leaning". There is a best power mixture setting, and a best economy mixture setting. Both are referenced to peak EGT, not an absolute EGT value.

Best power is approximately 100 to 125F rich of peak. Best economy is often given as about 50F lean of peak, but in reality can be anywhere from peak EGT to 100 LOP, the difference mostly being how slow you're willing to go to save gas.

Note that to use either of these settings, first you find peak EGT. Depending on probe location, the absolute value could be anywhere in a ballpark from 1250 to 1550F. Exactly how cool or hot doesn't matter. It's just a reference point.

There are only two circumstances in which you'll lean to a particular absolute EGT. The first is when using the "target EGT" method of leaning in the climb. Assuming a properly calibrated carb or FI, the EGT target is whatever absolute EGT you noted just after liftoff from the runway at full throttle. Don't need to note all of them; one will do. Later, as the system richens with increased altitude and/or power reduction, you'll lean to match the original target EGT.

The second is a bit more sketchy. Pilots will sometimes reach cruise altitude, make a power setting, then adjust mixture to reach a known absolute EGT value, or a known fuel flow. However, with few exceptions, those values were based on familiarity, and are known to match a previously established ROP or LOP value. For example, after 700 hours of bliss I know WOT and 2400 RPM at 9K to 11K altitude would put fuel flow in the very low 9 GPH range at peak EGT, so if I pull to a fuel flow in the 8's, I know I'm somewhere LOP and can't possibly hurt anything. It's a quick and dirty method, not particularly accurate, but it works if I want to make a rapid fuel conservation setting and move my wee brain along to some more pressing problem, like ATC or weather. I can go back and re-lean with more precision later.

According to Lycoming the yellow zone is 1400 and max is about 1450. But where is that measured from?

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Where did you read that? Best I know, Lyc publishes max turbine inlet temperature, but that's to spare the turbo, not the engine.

Lycoming #s

The 1400 / 1450 were, as I recall from the owners' manual provided by Lcoming when I purchased the engine.

SO, understanding the responses, I should lean until all the probes peak, noting each one's point; then, select one of them as representative and use it for leaning for either ROP or LOP.

Personally, I have never used - and was never taught - the LOP process; though I understand it. At this point, I guess I will re-program the EFIS for much higher EGT and then go about finding the peak points. After determining them, and re-programming my EFII computers, I'll focus on true fuel efficiency results.

Thanks for the feedback.

622BH said:

The 1400 / 1450 were, as I recall from the owners' manual provided by Lcoming when I purchased the engine.

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Sure would like to see that.

SO, understanding the responses, I should lean until all the probes peak, noting each one's point; then, select one of them as representative and use it for leaning for either ROP or LOP.

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Assuming you are leaning to peak from full rich....

Select the first cylinder to peak as your reference if setting best power mixture; all the other cylinders will be richer. Use the last cylinder to peak if setting best economy mixture; all the other cylinders will be leaner.

Thanks!

Dan,
Understood. On my engine, and it seems others are experiencing the same, cylinder # 1 is the hottest by at least 70 degrees. So it will be my "reference" cylinder for ROP. The others are all within 5 degrees of each other so I'll have to pay closer attention to which one is the laggard for LOP.

Thanks much to all repliers.

622BH said:

Dan,
Understood. On my engine, and it seems others are experiencing the same, cylinder # 1 is the hottest by at least 70 degrees. So it will be my "reference" cylinder for ROP. The others are all within 5 degrees of each other so I'll have to pay closer attention to which one is the laggard for LOP.

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Remember, it does not matter which is the hottest, i.e. indicates the highest absolute EGT value. It only matters which peaks first or last.

Bloody Amazing!

Bright and early this morning, before the OAT became blazing (for Oregon), I reprogrammed the EFIS EGT function to max at 2000 with Yellow a5 1700 and Red at 1750 (just a set of numbers to start).
Went flying and zeroed the EFII mixture knob. CHTs screamed up to 430+ but I ignored the EGT on takeoff. Upon leveling off at 3000 Ft, I began leaning the mixture - EGTs of course rose (but I was too amazed at the CHT to "capture" the EGT). The CHT plummeted to well below 350 and stayed there.
SO, for a bit more experimentation I really leaned and watched the CHT go down into the 320 ~ 330 range.

Damned! I am going to have to go play with this now to see what the EGT do - Those CHT are great compared to the last 20 hours of them going well above 400 in climb - even after new baffle material was installed.

Okay, I'm convinced - ignore the ### just focus on peaking and play accordingly.

622BH said:

Bright and early this morning, before the OAT became blazing (for Oregon), I reprogrammed the EFIS EGT function to max at 2000 with Yellow a5 1700 and Red at 1750 (just a set of numbers to start).

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Max and caution ranges on the EGT indication are useless...there is nothing that can make them go substantially higher than their usual peak values.

Went flying and zeroed the EFII mixture knob. CHTs screamed up to 430+....

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Which means you have baffle and seal problems, and/or somebody programmed your zeroed A/F ratio so you're in the 50 ROP EGT ballpark, and/or timing is advancing past 25 BTDC at full throttle.

First order of business is to check full throttle mixture at the zeroed knob setting. You want to be rich of peak 150F ~175F on all cylinders. Assuming a stock compression updraft 540, set the EFIS to record, and make a WOT takeoff with the mixture knob zeroed. Then (still recording) go to 3500, set up 2400/24, and very, very slowly lean a little bit at a time until all EGT's rise through peak and start back down on the LOP side. Return to base, download the data. Find the takeoff EGT for each cylinder, and the peak EGT for each cylinder. Subtract takeoff from peak. You want them all in the 150~175 range. If there is a lot of scatter (like one at 50, a few at 150, and one at 225), you have a tough problem. If they are closely grouped, but too lean (less than 150 degrees between takeoff and peak EGT), reprogram the zeroed air/fuel ratio to something richer and test again.

Those CHT are great compared to the last 20 hours of them going well above 400 in climb

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Keep in mind that running LOP offers low CHT, but doesn't result in rated power. Max power is found 125~150 ROP, and ultimately your goal is a cooling setup that will handle the horsepower you bought.